1. Field of the Invention
This invention relates to a focusing apparatus for a camera, and more particularly to a focusing operation changeover apparatus provided in a motor-driven auto focus type camera having a manual control device for manual focusing.
2. Description of the Related Art
Generally, an auto focus type camera has a motor for moving back and forth a group of photographic lenses in the direction of the optical axis thereof, whereby automatic focusing is accomplished through control of rotation of the motor in accordance with the range of distance from an object to the camera. However, manual focusing is required in some circumstances. To meet this requirement, a control ring connected to the photographic lenses for manual focusing is also provided on the lens barrel of a camera, and rotational operation of the control ring moves the photographic lenses back and forth in the direction of the optical axis thereof, whereby manual focusing is enabled.
With such a focusing apparatus, however, when automatic focusing is started, the manual control ring is also made to rotate simultaneously. Consequently, if the user's hand is touching the control ring at that time, the motor and intermediary connecting members have a tremendous load imposed on them, which disadvantageously causes failure and malfunction in focusing. In most cases, in order to avoid this, the manual control ring is disposed at such a position that it is most unlikely that the ring will be carelessly touched by the hand. But this results in another disadvantage in that operation of the ring is very difficult at the time of manual operation.
Also with, an interchangeable lens having a long lens barrel such as a telephoto lens, a member is often provided for the purpose of covering a manual control ring so as to avoid careless touching of the ring by a hand. However, with a device of this type, the member must be separately provided for covering the manual control ring and this member must be made longer and larger than the control ring, which needs to be a certain length from the view-point of operability of the ring at the time of manual operation. This means that the lens barrel must be made larger, which makes it difficult for photos to be taken while the camera is being held by hand. In addition, since at the time of an automatic focusing operation the motor is forced to rotate the large manual operation ring, it has a big load imposed on it, which also results in the disadvantage that there is a remarkable reduction in the life of the motor.